Chemical Changes of Some Important Sulfur-Containing Compounds During Crushing, Fermentation and Storage.
We used glutathione reaction product (GRP) and glutathione (GSH) labeled with radioactive 35S to study changes in these compounds during crushing and aging. During crushing GSH is converted to GRP as expected, but a large portion is oxidized to GSH disulfide (GSSG). After only 5 days incubation in a white wine, glutathione is largely oxidized to GSSG and also converted to a much less polar metabolite having an Rf of 0.62 on paper chromatography in 1-butanol/acetic acid/water (4:1:1 (V/V). During a 55 day aging study GRP appeared unchanged but GSH was converted to at least 4 other compounds, one of which was identified as GSSG. Since GRP might give rise to thiophenols during fermentation or aging we studied the sensory properties of two commercially available thiophenols. The sensory threshold for 4-hydroxythiophenol in a white wine was found to be lppm. The threshold for 4-mercapto toluene was estimated to be 0.06ppm. These results underline the importance of identifying the metabolic products of glutathione disulfide (GSSG) and glutathione reaction product (GRP) during fermentation and wine aging.